Generally, an internal combustion engine generates power by burning fuel and air received in a combustion chamber. Herein, an intake valve may be operated by a drive of a camshaft, and air flows into the combustion chamber while the intake valve is open. In addition, an exhaust valve may be operated by a drive of a camshaft, and air may be exhausted from the combustion chamber while the exhaust valve is open.
Meanwhile, optimal operations of the intake valve or the exhaust valve may be determined according to rotation speed of the engine. That is, lift and open/close timing of the valves may be properly controlled according to a rotation speed of the engine. A variable valve lift (VVL) apparatus has been developed in which the valves are operated with various lifts according to a rotation speed of the engine for realizing optimal operations of the valves according to a, or a changing, rotation speed of the engine. For example, there is a variable valve lift apparatus in which a plurality of cams for operating the valves at each different lift are provided to the camshaft, and the cam operating the valves is selected according to conditions.
When the plurality of cams is provided to the camshaft, however, the composition for selectively changing the cam to operate the intake valve or the exhaust valve may become complex, and an interference between the elements of the composition may occur. If the plurality of cams is respectively and independently operated for preventing interference between the elements of the composition, an additional constituent element is required for each cam for operating the cam such that costs may be increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.